1. Field of the Invention
This invention relates to electrical connectors and, more particularly, is directed toward a surface mount modular telephone-style jack which has protected, automatically aligned solder tails.
2. Description of Related Art
Telephone-style modular jacks are widely used in the computer networking and communications industries for interconnection of computers, modems, printers, and similar electronic equipment.
The demand for smaller packaging and more automated manufacturing has required the industry to increasingly use more surface mount components and the associated higher temperature board soldering processes in order to reduce the cost of an assembled printed circuit board and to improve the yield of electrically good circuit boards.
Two manufacturing processes which are increasingly used are IR and vapor phase soldering. In both processes, a metallic mask is used which contains cutouts of various shapes and sizes so that a paste of solder can be silk screened onto the circuit board surface. The cutouts correspond to locations of interconnections, either to solder tails of surface mount components or connectors or to metallic traces which form the electrical paths within a multi-layer circuit board. During the soldering process, the temperature of the chamber that the circuit boards pass through is of a sufficiently high temperature so that the solder paste on the board is increased to liquefy the solder. This allows the solder to wick onto any metallic surface in contact with the solder paste, forming an electrical connection which is typically referred to as a solder filet.
The IR soldering process uses radiant heat to heat both the surface mount components as well as the solder paste so that the solder tails are heated to a specific high temperature such that the liquefied solder is drawn to the solder tails, a process called wicking. The vapor phase soldering process heats a gaseous material which transfers the heat to each component as well as the solder paste, liquefying the solder paste in a similar manner to that described for IR soldering. As the circuit board passes from the highest temperature reflow chamber to a lower temperature, the solder solidifies. This produces solder filets.
Surface mount connectors typically use one of several configurations of solder tails to provide a means of forming an electrical connection from the printed circuit board to the contacts of the connector. One configuration is called a “J” tail, in which the solderable end of the contact is formed into the shape of the letter J. The curved bottom of the J is positioned such that the lowest point of the curved bottom is below the upper surface of the circuit board when the connector is fully seated on the circuit board. This would normally mean that the connector could not mount and grip the circuit board as the lowest solder tail point would meet and engage against the upper surface of the board, preventing the connector from being seated against the circuit board. However, the free end of the curve is not restrained, thereby allowing the curved surface to flex when engaging a rigid surface. By this flexing capability, the curve of the J, once the connector has been seated to the board, applies a force against the solder paste which resides on the surface of the circuit board. This applied force causes the curve of the J to press down against the circuit board and thereby remain fully within the solder paste, so that when the solder of the paste liquefies and wicks onto the solder tail, the lower part of the curve is surrounded by solder to produce a gas-tight solder joint. This is necessary to make a reliable electrical connection between the contact solder tail and the metal circuit of the circuit board. The gull wing is another widely used configuration for a solder tail of an electrical contact within a component. The gull wing has the approximate shape of the letter “L”, in which the foot of the L extends away from the component body. The foot may optionally angle slightly downward to make contact with the solder paste on the printed circuit board surface.
The gull wing style of solder tail is a rigid shape which does not flex, so that the foot resides in the solder paste due to the effect of surface tension, which keeps the foot in its position relatively constant to the paste. This style of solder tail is used primarily for integrated circuits (IC's) because they have low weight. The low weight of IC's allows the solder paste to exert a substantial hold on the component to retain the alignment of the gull wing's foot in alignment with the corresponding solder paste trace on the printed circuit board, which results in the solder wicking around the foot of the gull wing to produce a gas-tight connection to each solder tail.
One newer solder tail design is a variation of the gull wing to attempt to overcome the difficulties of the prior art solder tails when used with connectors. This newer solder tail can be described as a sweeping “L” because of its shape and its profile which resembles a sweep elbow. The vertical portion of the L is reduced in length so that this portion is shorter than the sweep and the foot taken together. The sweep typically has a contained angle greater than ninety degrees so that the foot of the solder tail angles down toward the printed circuit board. As the sweep is curved in its shape, it has an inherent spring quality so that it can maintain the foot in constant engagement with the solder paste on the printed circuit board. Because of the spring properties, the foot is held in the solder paste so that during solder reflow, the solder flows around the tip of the foot and forms a gas-tight connection to the solder tail foot.
This design, while providing an improvement over prior art designs, still has two major deficiencies of previous solder tail designs. In all prior art designs, a portion of the solder tail extends beyond the rear wall of the connector. This extended portion is beyond the protective boundary of the connector housing, and is exposed to possible mechanical damage or alteration of alignment from its original alignment. Damage or misalignment could occur during packaging of the connectors, or during stacking or handling during shipment or warehousing, during removal of the connectors from their packaging containers, or during pickup and handling by automated pick and place equipment.
Due to the close spacing of components and the density of connections on surface mount printed circuit boards, alignment of solder tails to solder paste is critical and has very low margin for error. Even a slight misalignment of the solder tails can easily result in a high resistance, incomplete connection, or a failed, non-electrical connection, or in a bridged connection between two adjacent solder tails from solder that bridges over to both tails. The fully assembled printed circuit board that is produced is now defective because of the connector and it must be scrapped.
Another deficiency is the absence of a means of controlling the alignment of the solder tails to maintain a high degree of alignment accuracy. The yield of defect free printed circuit boards is in direct proportion to the relative alignment of a solder tail to its corresponding solder paste pattern on the printed circuit board. As previously described, the density of traces on the printed circuit board is becoming greater with less clearance space between each such trace and therefore less tolerance is available for aligning a solder tail.
Various approaches have been used to try and overcome these deficiencies in the designs of surface mount connectors, such as is taught in the following patents: U.S. Pat. Nos. 4,992,052 and 5,413,491, the disclosure of which are specifically incorporated herein by reference. U.S. Pat. No. 5,413,491 contains two rows of contacts, in which each contact is comprised of a mating portion designed to engage a square post mateable, and a solder tail portion in the configuration of a gull wing. The foot of each gull wing portion is angled slightly downward to engage into the solder paste and against the surface of the printed circuit board when the connector is fully seated against the printed circuit board. The foot of each gull wing projects out beyond the side wall of the connector body that retains the contact so that the free end of the foot is exposed to external damage.
A primary objective of U.S. Pat. No. 4,992,052 is to provide an improved gull wing type of contact which utilizes an angled transition portion from the start of the foot of the “L” to a point more than half the length of the foot. The solder portion of the foot is less than the angled portion and is aligned at an angle from the angled portion such that the solder portion is substantially parallel to the surface of the printed circuit board. The angled transition portion provides spring pressure engagement through the solder portion by holding the solder portion against the surface of the printed circuit board and within the solder paste.
While the recent prior art makes some improvements toward addressing the problem of providing precise alignment of each solder tail to the solder paste pattern that corresponds to each solder tail, and provides for some additional spring engagement of each solder tail to its corresponding solder paste area, it remains deficient in providing the high precision of alignment of the solder tail to its corresponding solder paste, and in protecting the solder tails from possible alignment or mechanical damage.